Switching regulator

ABSTRACT

A switching regulator includes: a boost chopper circuit A including a plurality of inductances 2, 3, 4 and 5 which are connected in parallel with a D.C. power supply 1 for boosting the D.C. power supply 1, a plurality of commutating diodes 6, 7, 8 and 9 which are connected to output sides of those inductances 2, 3, 4 and 5, respectively, a plurality of switching elements 10, 11, 12 and 13 for connecting the D.C. power supply 1 and nodes between the respective inductances 2 to 5 and the respective diodes 6 to 9 in a short-circuiting manner, and a smoothing capacitor 14 connected in series to a combined output section of those diodes 6 to 9; a control circuit 15 for controlling the on/off operation of those switching elements 10 to 13; and a load 16 connected in parallel with the smoothing capacitor 14. The plurality of switching elements 10 to 13 repeatedly operate while the operation of the plurality of switching elements 10 to 13 is sequentially delayed by a predetermined period of time.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a switching regulator used as powersupply for an inverter circuit for driving a electric motor by boostinga low voltage (24 V, 48 V, etc.) of a battery mounted on an electricvehicle, as a power supply of a solar cell for high output, or forcompletely consuming an energy of a super capacitor or the like.

2. Description of the Related Art

Up to now, there is one type of switching regulators for obtaining anoutput voltage higher than that of an input voltage, which is made up ofa boost chopper circuit, for example, as shown in FIGS. 7 and 8.

In FIG. 7, an inductance 2 is connected in series to a plus side of aD.C. power supply 1, an anode side of a diode 6 is connected to anoutput side of the inductance 2, and a cathode side of the diode 6 isconnected to a node 50 at which the smoothing capacitor 14 and a load 16are connected in parallel. Then, in order to hold a voltage across theload 16 constant, there is provided a control circuit 15 for controllingthe on/off operation of a switching element (FET) 10 that short-circuitsa node between the inductance 2 and the diode 6 and a minus side of theD.C. power supply 1.

The control circuit 15 operates so that in an on-state of the switchingelement (FET) 10, the load 16 is driven by a voltage VI of the D.C.power supply 1 while a magnetic energy is stored in the inductance 2.Then, when the switching element (FET) 10 becomes in an off-state, themagnetic energy stored in the inductance 2 and the voltage VI of theD.C. power supply 1 are superimposed on each other to drive the load 16.

FIG. 8 shows a circuit structure in which a circuit consisting of aninductance 26, a diode 30, a switching element (FET) 22 and a smoothingcapacitor 34 which is identical in structure with the circuit of FIG. 7is connected in series to the circuit of FIG. 7. In the figure, when theswitching elements (FETs) 10 and 22 are in the on-state, the load 16 isdriven by the voltage VI of the D.C. power supply 1 while a magneticenergy is stored in the inductances 2 and 26. Then, when the switchingelements (FETs) 10 and 22 become in the off-state, the magnetic energystored in the inductances 2 and 26 and the voltage VI of the D.C. powersupply 1 are superimposed on each other to drive the load 16.

In both of the above two circuits shown in FIGS. 7 and 8, because acurrent I_(c1) or I_(c2) flowing in the capacitor 14 or 34 becomes alarge triangular-wave ripple current, a current of several tens amperesor more flows in the capacitor 14 or 34 particularly when the load 16 islarge in capacitance (1 kW or more), to thereby make the heating of thesmoothing capacitors 14 and 34 high. As a result, there aredisadvantageous in that not only the smooth capacitors must be madelarger in size but also the lifetime becomes shorter.

Also, when the switching elements (FETs) 10 and 22 are in the on-state,that is, when the magnetic energy is stored in the inductances 2 and 26,the output voltage is equal in value to the input voltage VI. Therefore,a discharge energy from the smoothing capacitors is relied on in orderto obtain a large output voltage, and large-scaled smoothing capacitorsare required. This causes not only that the above disadvantages are maderemarkable but also that in the case where the energy consumption of theload is particularly large, the magnetic energy stored in theinductances 2 and 26 is completely discharged, to thereby disable theload to be continuously driven. Thus, there is room for improvement.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve the aboveproblems, and therefore an object of the present invention is to providea switching regulator which is capable of supplying a large output whilepreventing a smoothing capacitor from being increased in size, and alsowhich is capable of preventing a short lifetime and continuously drivinga load.

In order to achieve the above object, according to the presentinvention, there is provided a switching regulator, comprising: a boostchopper circuit including a plurality of inductances connected inparallel with a D.C. power supply for boosting the D.C. power supply; aplurality of commutating diodes connected to output sides of saidinductances, respectively, a plurality of switching elements forconnecting said D.C. power supply and a node between each of saidinductances and each of said diodes in a short-circuiting manner, and asmoothing capacitor connected in series to a combined output section ofsaid plurality of diodes; a control circuit for controlling the on/offoperation of said plurality of switching elements; and a load connectedin parallel with said smoothing capacitor; wherein said plurality ofswitching elements repeatedly operate while the operation of saidplurality of switching elements is sequentially delayed by apredetermined period of time.

Because the plurality of switching elements repeatedly operate while theoperation of the plurality of switching elements is sequentially delayedby a predetermined period of time, a large output (energy) can beobtained in comparison with a switching regulator in which energiesstored in other inductances not corresponding to a specific switchingelement when the specific switching element is in an on-state aresequentially outputted by switching the specific switching element fromthe on-state to an off-state to boost an output voltage by a singleswitching element. Also, a current flowing in the smoothing capacitorcan be smoothed, and even in the case where an energy consumption of theload is particularly large, the load can be continuously driven byadjusting the on/off period of the switching element. A larger output(energy) can be obtained as the number of inductances increases.

The above control circuit comprises a PWM control circuit that controlsthe on-period of the plurality of switching elements in order to holdavoltage value of the load constant. Alternatively, a micro-computer orthe like may be employed for control.

With an arrangement in which the respective inductances are made up ofinsulating flyback transformers each consisting of a primary winding anda secondary winding, if the number of turns of the primary winding andthe number of turns of the secondary winding are altered, the outputvoltage can be not only boosted but also dropped with respect to theinput voltage.

Because a plurality of boost chopper circuits structured as describedabove are connected in series, and all of the switching elements ofthose boost chopper circuits are connected to a single control circuitso as to be on/off-controlled, a large output (energy) can be obtainedin comparison with a switching regulator in which a single boost choppercircuit is driven. Moreover, if all of the switching elements areon/off-controlled by a single control circuit, the circuit can besimplified.

The above and other objects and features of the present invention willbe more apparent from the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a first specific structure of aswitching regulator;

FIG. 2 is a diagram showing waveforms of currents flowing in inductancesand waveforms of an input current;

FIG. 3 is a timing chart of the switching regulator;

FIG. 4 is a circuit diagram showing a specific structure of a PWMcontrol circuit;

FIG. 5 is a circuit diagram showing a second specific structure of theswitching regulator;

FIG. 6 is a circuit diagram showing a third specific structure of theswitching regulator;

FIG. 7 is a circuit diagram showing a first conventional specificstructure of the switching regulator;

FIG. 8 is a circuit diagram showing a second conventional specificstructure of the switching regulator; and

FIG. 9 is a graph showing an energy stored in inductances and a currentflowing in a smoothing capacitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a description will be given in more detail of preferred embodimentsof the present invention with reference to the accompanying drawings.

FIG. 1 shows a switching regulator according to the present invention.

The switching regulator, as shown in FIG. 1, includes: a boost choppercircuit A including four inductances 2, 3, 4 and 5 which are connectedin parallel with a D.C. power supply 1 for boosting the D.C. powersupply 1, four commutating diodes 6, 7, 8 and 9 which are connected tooutput sides of those inductances 2, 3, 4 and 5, respectively, fourfield effect transistors 10, 11, 12 and 13 (hereinafter referred to as"FETs") serving as switching elements for connecting the D.C. powersupply 1 and nodes between the respective inductances 2 to 5 and therespective diodes 6 to 9 in a short-circuiting manner, and a smoothingcapacitor 14 connected in series to a combined output section of thosefour diodes 6 to 9; a control circuit 15 for controlling the on/offoperation of those four FETs 10 to 13; and a load 16 connected inparallel with the smoothing capacitor 14. The number of the inductancesmay be two, three, five or more for implementation. The number ofswitching elements is altered in correspondence with the number ofinductances. The switching elements may be formed of various elementssuch as transistors or insulated gate bipolar mode transistors (IGBTs)other than FETs.

The control circuit 15 is designed to control the on/off operation ofthe four FETs 10 to 13 on the basis of a variation in the terminalvoltage of the load 16, and specifically formed of a PWM control circuitthat holds a frequency constant and controls the on-period (pulse width)of the FETs 10 to 13, to thereby hold an output voltage constant. Inother words, in the case where a voltage across the load 16 becomeslower than a predetermined voltage, the on-periods of the FETs 10 to 13are lengthened so as to obtain a large output voltage. On the contrary,in the case where the voltage across the load 16 becomes higher than thepredetermined voltage, the on-periods of the FETs 10 to 13 are shortenedso as to obtain a small output voltage. As a result, the output voltagecan be always held constant regardless of a fluctuation of the voltageacross the load 16. The four inductances 2 to 5 are repeatedly operatedwhile the operation of the four inductances 2 to 5 is sequentiallydelayed by a predetermined period of time so that magnetic energiesstored in the inductances 2 to 5 are superimposed on an input voltage VIto drive the load 16. As a result, not only a ripple current can beprevented from occurring but also an output can be remarkably improved.In addition, the smoothing capacitor 14 small in capacitance can beemployed.

The PWM control circuit 15 is made up of, as shown in FIG. 4, anoscillating circuit 17 for generating clock pulses, a counter 18 forcounting the clock pulses from the oscillating circuit 17, a pluralityof triangular-wave generating circuits 19 for appropriately generatingtriangular waves according to information from the counter 18, aplurality of differential amplifiers 20 for comparing voltages fromthose triangular-wave generating circuits 19 with a detected outputvoltage (a detected load voltage) to generate outputs, and gate drivers21 for driving the gates of the FETs 10 to 13 according to outputs fromthose differential amplifiers 20. The PWM control circuit 15 is notlimited to the above structure, but the on-period (pulse width) of theFETs 10 to 13 may be controlled by a micro-computer.

The operation of the switching regulator thus structured will bedescribed. As shown in FIG. 3, when a clock pulse of the predeterminednumber (a first pulse) among clock pulses generated from the oscillatingcircuit 17 rises, a voltage is applied to the gate of the FET 10 to makethe FET 10 in an on-state. In this situation, the D.C. current I allowsa current i₁, that is, a current indicated by a triangular-wave currentA for exciting the inductance 2 shown in FIG. 2 to flow. At the sametime, the application of a voltage to the gate of the FET 11 which is inthe on-state is interrupted to make the FET 11 in an off-state. In thissituation, a voltage B₁, shown in FIG. 3 is moved to the smoothingcapacitor 14 in a forward direction of the diode 7 with a magneticenergy stored in the inductance 3 as a flyback voltage. A currentflowing in this situation is indicated by B₁ in FIG. 2. A relation thatan area of an energy B stored in the inductance 3 is identical with anarea of an energy B₁ discharged as the flyback voltage is satisfied, andthe respective relationships between A and A₁, C and C₁, and D and D₁generated by the FETs 10, 12 and 13 which will be described later arealso identical with the above relationship in theory. Then, in thefigure, when a second clock pulse rises, a voltage is applied to thegate of the FET 11 that gets in the off-state to make the FET 11 in theon-state. In this situation, the D.C. current I allows a current i₂,that is, a current indicated by a triangular-wave current B for excitingthe inductance 3 shown in FIG. 2 to flow. At the same time, theapplication of a voltage to the gate of the FET 12 which is in theon-state is interrupted to make the FET 12 in the off-state. In thissituation, a voltage C₁ shown in FIG. 3 is moved to the smoothingcapacitor 14 in a forward direction of the diode 8 with a magneticenergy stored in the inductance 4 as a flyback voltage. Sequentially, inthe figure, when a third clock pulse rises, a voltage is applied to thegate of the FET 12 that gets in the off-state to make the FET 12 in theon-state. In this situation, the D.C. current I allows a current i₃,that is, a current indicated by a triangular-wave current C for excitingthe inductance 3 shown in FIG. 2 to flow. At the same time, theapplication of a voltage to the gate of the FET 13 which is in theon-state is interrupted to make the FET 13 in the off-state. In thissituation, a voltage D₁ shown in FIG. 3 is moved to the smoothingcapacitor 14 in a forward direction of the diode 9 with a magneticenergy stored in the inductance 5 as a flyback voltage. Then, in thefigure, when a fourth clock pulse rises, a voltage is applied to thegate of the FET 13 that gets in the off-state to make the FET 13 in theon-state. In this situation, the D.C. current I allows a current i₃,that is, a current indicated by a triangular-wave current C for excitingthe inductance 5 shown in FIG. 2 to flow. At the same time, theapplication of a voltage to the gate of the FET 10 which is in theon-state is interrupted to make the FET 10 in the off-state. In thissituation, a voltage A₁ shown in FIG. 3 is moved to the smoothingcapacitor 14 in a forward direction of the diode 6 with a magneticenergy stored in the inductance 2 as a flyback voltage. With the aboveoperation, one cycle is completed. That is, four clock pulses form oneperiod, and every time one clock pulse rises, one specific FET 10, 11,12 or 13 is sequentially made in the on-state, and when the FET 10, 11,12 or 13 which is sequentially made in the on-state is made in theoff-state once when a predetermined period (4 periods) elapses, andevery time a succeeding clock pulse rises, the FET 10, 11, 12 or 13which is made in the off-state is sequentially made in the on-state.This operation is repeated.

In this embodiment, there is applied a system in which for prevention ofan over-excitation of the inductances, the on-periods of the respectiveFETs 10 to 13 are set as 70% at maximum, and the off-periods thereof areset as 25% at minimum to stabilize the operation, and the on-periods andoff-periods of the respective FETs 10 to 13 are adjustably changedaccording to a fluctuation of the output voltage. That is, therespective FETs 10 to 13 are controlled by the PWM control circuit 15 soas to satisfy a relationship of output voltage V₀ =(FET_(ON)+FET_(OFF))/FET_(OFF) ×VI. If a loss is ignored, in the case where theon-period is set as 75%, V₀ =4VI is satisfied. FIG. 3 shows a case inwhich the on-period is set as 75%. The on-periods of the respective FETs10 to 13 are set as 75% at maximum, and the off-periods thereof are setas 20% at minimum for prevention of an over-excitation of theinductances. However, they are not limited to those numeral values.

In this embodiment, all the pulse widths of the clock pulses are set tobe identical with each other. However, the pulse width may be changedfor each of the clock pulses, or only the pulse width of a specificclock pulse may be changed for implementation. Also, in this embodiment,the values of the respective voltages A₁, B₁, C₁ and D₁ are identicalwith each other. However, the values of the respective voltages A₁, B₁,C₁ and D₁ may be entirely or partially different from each other.Further, although the prevention of gaps between the respective voltagesA₁, B₁, C₁ and D₁ from occurring is ideal, such gaps may occur with thelimit that no problem occurs.

Accordingly, as described above, the on-periods and the off-periods ofthe four FETs 10 to 13 are adjusted so that as shown in FIG. 3, theoutput voltage V₀ becomes a total of an area of the energies A, B, C andD stored in the respective inductances 2 to 5 and an area of energiesA₁, B₁, C₁ and D₁ discharged by the respective inductances 2 to 5, thusbeing capable of always ensuring a given output voltage.

Then, the input current i₀ flowing in the D.C. power supply 1 becomes i₀=i₁ +i₂ +i₃ +i₄ as shown in FIG. 2, thereby enabling a flat D.C. currentwithout any ripple components to flow. In the figure, there are shownthe mean values i₁₀, i₂₀, i₃₀ and i₄₀ of the currents i₁, i₂, i₃ and i₄which flow in the respective inductances 2 to 5, and a total of thosemean values i₁₀, i₂₀, i₃₀ and i₄₀ represent the input current i₀.

The above switching regulator may be structured as shown in FIG. 5. Thatis, two boost chopper circuits A are connected in series and connectedto the above PWM control circuit 15 for controlling the on/off operationof all of the switching elements 10 to 13 and 22 to 25 of those boostchopper circuits A.

The boost chopper circuit A on the left side of both the boost choppercircuits A includes four inductances 2, 3, 4 and 5, four commutatingdiodes 6, 7, 8 and 9 which are connected to output sides of thoseinductances 2, 3, 4 and 5, respectively, four switching elements 10, 11,12 and 13 for connecting the D.C. power supply 1 and nodes between therespective inductances 2 to 5 and the respective diodes 6 to 9 in ashort-circuiting manner, and a smoothing capacitor 14 connected inseries to an output side of those four diodes 6 to 9. The boost choppercircuit A on the right side of both the boost chopper circuits Aincludes four inductances 26, 27, 28 and 29, four commutating diodes 30,31, 32 and 33 which are connected to output sides of those inductances26, 27, 28 and 29, respectively, four switching elements 22, 23, 24 and25 for connecting the D.C. power supply 1 and nodes between therespective inductances 26 to 29 and the respective diodes 30 to 33 in ashort-circuiting manner, and a smoothing capacitor 34 connected inseries to an output side of those four diodes 30 to 33.

The switching regulator structured as described above can obtain anoutput voltage as high as the number of inductances is more than thatshown in FIG. 1. The smoothing capacitor 14 shown in the figure isprovided for eliminating noises and can be omitted for implementation.

The operation of the switching regulator shown in FIG. 5 will be brieflydescribed. Because the number of inductances is twice, for example, theoutput voltage V₀ can be always held constant by controlling the on/offoperation of four pairs of inductances 2, 26, 3, 27, 4, 28, 5 and 29according to four clock pulses as in the above manner so that in a statewhere a pair of inductances 2 and 26 are off according to a clock pulsesignal of the specific number, other three pairs of inductances 3, 27,4, 28, 5 and 29 are in the on-state.

The above switching regulator may be structured as shown in FIG. 6. Inother words, with the inductances 2 to 5 being made up of insulatingflyback transformers each consisting of a primary winding and asecondary winding, when the number of turns of the primary winding isset to be less than the number of turns of the secondary winding, theoutput voltage can be allowed to rise with respect to the input voltage.On the contrary, when the number of turns of the primary winding is setto be more than the number of turns of the secondary winding, the outputvoltage can be allowed to drop with respect to the input voltage. Inother words, if the number of turns of the primary winding and thenumber of turns of the secondary winding are changed, currents i₁₁, i₁₂,i₁₃ and i₁₄ flowing in the secondary inductances can be changed withrespect to currents i₁, i₂, i₃ and i₄ flowing in the primary inductancesso that the output voltage is allowed to rise or drop with respect tothe input voltage.

According to the first aspect of the present invention, since a currentflowing in the smoothing capacitor can be flattened without any ripples,the lifetime can be prevented from being shortened due to heating of thesmoothing capacitor. Also, because the energies stored in a plurality ofinductances are sequentially discharged, not only the output voltage canbe always held constant but also the output voltage can be structured ina high output, thereby being capable of downsizing the smoothingcapacitor. Moreover, even when the energy consumption of the load islarge, the load can be continuously driven by adjusting the on/offperiod of the switching element, thereby being capable of providing aswitching regulator high in reliability. A higher output can be obtainedas the number of inductances increases.

According to the second aspect of the present invention, there isadvantageous in that control can be digitalized by conducting PWMcontrol using a micro-computer, and if various control is conducted bysoftware, a high output power supply can be provided which enablesdigital control as a power supply for an electric automobile and a robotexpected in the future.

According to the third aspect of the present invention, the outputvoltage can be allowed to rise and drop only by changing the number ofturns of the primary winding and the number of turns of the secondarywinding. A range where the circuit is useable can be expanded. Inaddition, a variation width of the value of the output voltage can bechanged freely only by changing the number of turns of the primarywinding and the number of turns of the secondary winding.

According to the fourth aspect of the present invention, when aplurality of boost chopper circuits are connected in series, ahigh-voltage and large-capacitance output (energy) can be obtained incomparison with a switching regulator in which a single boost choppercircuit is driven, thereby being capable of expanding a range where theoutput is useable. In addition, if all of the switching elements areon/off-controlled by a single control circuit, the circuit can besimplified, thereby being capable of reducing the costs.

The foregoing description of a preferred embodiment of the invention hasbeen presented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and modifications and variations are possible in light of theabove teachings or may be acquired from practice of the invention. Theembodiment was chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto, and their equivalents.

What is claimed is:
 1. A switching regulator, comprising:a plurality ofboost chopper circuits connected in series, each said boost choppercircuit including a plurality of inductances connected in parallel witha D.C. power supply for boosting the D.C. power supply, a plurality ofcommutating diodes connected to output sides of said inductances,respectively, a plurality of switching elements for connecting said D.C.power supply and a node between each of said inductances and each ofsaid diodes in a short-circuiting manner, and a smoothing capacitorconnected in series to a combined output section of said plurality ofdiodes; a single control circuit for controlling the on/off operation ofsaid plurality of all switching elements of said plurality of boostchopper circuits with a series of clock pulses, each clock pulse beingassociated with a specific switching element; and a load connected inparallel with said smoothing capacitor, wherein each of said switchingelements is made in an on-state one after another whenever the clockpulse associated with said switching element rises, and each switchingelement in an on-state is turned off after a predetermined cycle, andeach switching element in an off-state is made in an on-state again oneafter another whenever the next clock pulse associated with saidswitching element rises, such that at least two switching elements arealways in an on-state.
 2. A switching regulator as claimed in claim 1,wherein said control circuit comprises a PWM control circuit thatcontrols the on-period of the plurality of switching elements to hold avoltage value of the load constant.
 3. A switching regulator as claimedin claim 1, wherein said inductances comprise insulating flybacktransformers each consisting of a primary winding and a secondarywinding.
 4. A switching regulator as claimed in claim 1, wherein aplurality of said boost chopper circuits are connected in series, andall of said switching elements of said boost chopper circuits areconnected to said single control circuit to control the on/off operationof all of said switching elements.
 5. A switching regulator as claimedin claim 1, wherein said on-state time is set at a maximum of 75% andsaid off-state time is set at a minimum of 25% when the number of saidinductances is four.